title: The presence of ultralow densities of nanocrystallites in amorphous poly(lactic acid) microspheres.
abstract: Ultralow densities of crystalline nanospheres have been detected in amorphous polymer microspheres by utilizing the unique sensitivity of second-order nonlinear optical techniques to anisotropy. Vibrational sum frequency scattering (SFS) and X-ray diffraction (XRD) are used to quantify the crystallinity of amorphous poly(d,l-lactic acid) microspheres. While XRD does not display any crystallinity for the microspheres, SFS spectra and patterns are reminiscent of a heterogeneous microsphere that contains small crystalline domains. Nonlinear light scattering theory was used to model the data, and an average domain radius of 147 ± 65 nm was obtained. The degree of crystallinity (0.2%) was estimated by comparing XRD and SFS data obtained from the amorphous microspheres to similar data obtained from crystalline microspheres. We estimate a detection limit of 0.002% for SFS.
authors.affiliation: Laboratory for Fundamental Biophotonics (LBP), Institute of Bioengineering (IBI), School of Engineering (STI), École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland.
authors.forename: Hilton B
authors.initials: HB
authors.lastname: de Aguiar
authors.forename: Alex G F
authors.initials: AG
authors.lastname: de Beer
authors.forename: Sylvie
authors.initials: S
authors.lastname: Roke
mesh_terms: D019344:Lactic Acid / Q000737:chemistry*; D008863:Microspheres; D053758:Nanoparticles / Q000737:chemistry*; D011091:Polyesters; D011108:Polymers / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D011091:Polyesters; D011108:Polymers; D014867:Water; D019344:Lactic Acid; C033616:poly(lactide)